Method of forming a transformer assembly

ABSTRACT

The present disclosure provides methods and techniques associated with a planar transformer for an apparatus. The planar transformers include a substrate carrying electronic components and a continuous core that is formed by distributing the encapsulant material uniformly around the substrate unit to define a consistent cross-sectional area for the magnetic path. The electronic components include primary windings and secondary windings associated with the transformer. In some embodiments, the encapsulant material is molded to seals air gaps to the substrate unit.

This application is a continuation of U.S. patent application Ser. No.15/378,222, filed Dec. 14, 2016, now abandoned, and which is adivisional of U.S. patent application Ser. No. 13/798,776, filed Mar.13, 2013, now abandoned, which are incorporated herein by reference intheir entireties.

FIELD

The present disclosure generally relates to an implantable medicaldevice, and more particularly to transformer assemblies incorporatedinto the medical device and associated methods for making thetransformer assemblies.

BACKGROUND

An implantable medical device (IMD) such as an implantable cardioverterdefibrillator (ICD) may be used to deliver shock therapy to a patient'sheart in order to perform therapies such as defibrillation andcardioversion. Some ICDs may also provide several different pacingtherapies, including such therapies as cardiac resynchronization,depending upon the needs of the user or patient and the medicalcondition of the patient's heart. For convenience, all types ofimplantable medical devices will be referred to herein as IMDs, it beingunderstood that the term, unless otherwise indicated, is inclusive of animplantable device capable of administering a cardiac therapy.

In IMDs that deliver defibrillation or cardioversion therapies, it isnecessary to develop high voltages, perhaps 750 volts or more, withinthe IMD in order to administer a sufficient shock to a patient tocorrect an arrhythmia or a fibrillation, particularly a ventricularfibrillation. To generate such high voltages, a battery and capacitors(usually two) may be used. Preferably, the capacitors are fully chargedbefore defibrillation or cardioversion therapies are delivered. In someconfigurations, flyback and non-flyback transformers are employed toincrementally charge the defibrillation capacitors prior to therapydelivery. Once the capacitors are charged, the defibrillation orcardioversion therapy is delivered via insulated gate bipolartransistors or other suitable semiconductor switches that are switchedon and off to apply charge stored in the capacitors in biphasic pulsewaveform to the heart.

Because IMDs are implanted subcutaneously, it is preferable that the IMDis sized as small as possible to reduce any discomfort that the patientmay experience post-implantation. Conventionally, however, some of theelectronic components that are housed within the IMD are relativelylarge. For example, transformers are used which have coil and coremembers that are physically separate from other IMD components. Althoughthese conventional transformers have been reliable, they occupy aconsiderable amount of space within the IMD.

Accordingly, it remains desirable to provide a method and apparatus fordecreasing the size of a transformer for use in an implantable medicaldevice, while maintaining its reliability.

SUMMARY

The present disclosure is directed to an IMD having a hermeticallysealed chamber defined by a hermetically sealed housing. Containedwithin the housing is a power source, a capacitor bank for storing acharge from the power source, and electronic circuitry coupled to thepower source and the capacitor bank for charging the capacitor bankthrough a transformer and for discharging the capacitor-bank charge intoselected body tissue.

In an embodiment, techniques are described for making transformerassemblies that are miniaturized sufficiently to fit within small spacesof the housing cavity. The transformer assemblies are provided having asubstrate unit that is sandwiched between a pair of cores including anupper and a lower core, both of which may be comprised of a magneticmaterial. In one embodiment, a transformer assembly includes a substrateunit having electronic components arranged therein. The electroniccomponents arranged in the substrate unit may include primary andsecondary windings. A first of the pair of cores, for example, the uppercore, is disposed on a top surface of the substrate unit. A second ofthe pair of cores, for example the lower core, is disposed on a bottomsurface of the substrate unit. The transformer further includes anencapsulant material that is dispensed over the upper core and withinthe gaps between the upper core and the electronic components of thesubstrate unit. The encapsulant material functions to couple andpermanently position the upper core to the top surface. Similarly, thelower core may be permanently positioned on the bottom surface withencapsulant material, while in other embodiments, an adhesive materialmay be applied to affix the lower core to the substrate unit. In anembodiment, the encapsulant material is formed to expose a surface ofthe upper and/or lower cores, such surface being parallel to the topsurface of the substrate unit.

In a second embodiment, a transformer assembly includes a substrate unithaving electronic components and including primary and secondarywindings embedded within the substrate unit. The substrate unit may befully (or substantially) encapsulated by a core that includes an uppercore and a lower core. The upper and lower cores may be assembled toeliminate an air gap therebetween. For example, the upper and lowercores may be formed in a molding process from a liquefied encapsulantmaterial that is dispensed to encapsulate the substrate unit.

According to an embodiment of the disclosure, a method for forming atransformer assembly is disclosed. In accordance with the method, asubstrate having a plurality of substrate units is provided with each ofthe substrate units including electronic components. In an embodiment,the electronic components include primary and secondary windingsassociated with a transformer. The substrate is mounted to a firstsurface of an adhesive material and a carrier plate is mounted to asecond surface of the adhesive material. An upper core is placed overeach of the substrate units. An encapsulation of the assembly includingthe substrate and the upper core is performed by molding to continuouslyencapsulate the portion of the assembly adhered to the first surface ofthe adhesive material. In an embodiment, molding includes dispensing anencapsulant material between the air gaps formed by the electroniccomponent and the upper core of each of the substrate units. Thesubstrate is subsequently detached from the adhesive material and alower core is bonded to each of the substrate units. In an embodiment,the plurality of substrate units are separated into individual units.

In another embodiment, a method for manufacturing a transformer assemblyincludes encapsulating a substrate unit with an encapsulant material.The substrate unit includes electronics and primary and secondarywindings for the transformer. The encapsulant material is formed as aunitary/continuous member to define a homogeneous core of thetransformer, with the windings and/or electronics being embedded withinthe core. In one embodiment, the core may be formed by distributing theencapsulant material uniformly around the windings to define aconsistent cross-sectional area. The encapsulant material may include apolymer bonded magnetic compound.

BRIEF DESCRIPTION

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments will hereinafter be described in conjunctionwith the appended drawings wherein like numerals/letters denote likeelements, and:

FIG. 1 illustrates an implantable system in accordance with oneexemplary embodiment;

FIG. 2 depicts a simplified block diagram of exemplary circuitry 30 thatmay be housed within the IMD 20;

FIG. 3A illustrates a cross-sectional view of a transformer assembly inaccordance with an embodiment;

FIG. 3B illustrates a cross-sectional view of an alternative transformerassembly;

FIG. 4 illustrates a cross-sectional view of another alternativetransformer assembly;

FIGS. 5A to 5E depict cross-sectional views of a transformer assemblysuch as that shown in any one of FIGS. 3A and 3B associated with amethod for fabrication of the transformers;

FIGS. 6A-6C depict cross-sectional views of a transformer assembly suchas that shown in any one of FIGS. 3A and 3B associated with analternative method for fabrication of the transformers; and

FIGS. 7A and 7B depict cross-sectional views of a transformer assemblysuch as that shown in any one of FIG. 4 associated with an alternativemethod for fabrication of the transformers.

DETAILED DESCRIPTION

The following detailed description is illustrative in nature and is notintended to limit the embodiments of the invention or the applicationand uses of such embodiments. Furthermore, there is no intention to bebound by any expressed or implied theory presented in the precedingtechnical field, background, brief summary or the following detaileddescription.

In the present disclosure, the inventors have disclosed deviceassemblies and methods for construction associated with transformers.The transformer is one of the constituent electrical components of animplantable medical device and is utilized to convert low batteryvoltage into a high voltage that is sufficient to charge capacitors thatare used to deliver an electrical stimulating therapy. Conventionaltransformers are built by winding a wire onto a toroid magnetic core.Due to the relatively small size, some of the winding process is manual,which results in significant cost and performance variability. Theinventors have observed that the conventional transformer is generallythe largest and tallest component in relation to other electricalcomponents of the implantable medical device. The inventors have alsoobserved that the rigidity and fragility of conventional discrete corescreates challenges in reducing the dimensions of the transformer. Inaccordance with embodiments of the present disclosure, processingtechniques and/or materials are described that provide the ability toachieve transformer packages with desired dimensions that may be smallerthan those that are achievable with the conventional discrete cores.

FIG. 1 illustrates an implantable system in accordance with oneexemplary embodiment of the disclosure. An implantable medical device(IMD) 20 is implanted in a body 10 near a heart 12. IMD 20 includescircuitry, a battery and other components that are contained within ahermetically sealed, biologically inert outer canister or housing thatmay be conductive so as to serve as a pace/sense electrode in thepacing/sensing circuit. One or more leads, collectively identified withreference numeral 22, electrically couple to the IMD 20 and extend intothe heart 12. In the case where device 20 is a pacemaker, leads 22 arepacing and sensing leads to sense electrical signals attendant to thedepolarization and repolarization of the heart 12 and provide pacingpulses in the vicinity of the distal ends thereof. One or more exposedconductive pace/sense electrode(s) for sensing electrical cardiacsignals or delivering electrical pacing pulses to the heart 12 aredisposed at or near the distal ends of the leads 22. The leads 22 may beimplanted with their distal ends situated in the atrium and/orventricles of the heart 12 or elsewhere in cardiac blood vessels inoperative relation with a heart chamber. The leads 22 can also carryother sensors for sensing cardiac physiologic data, e.g. pressure,temperature, impedance, pH, blood gas, acceleration, etc.

IMD 20 may also be a pacemaker/cardioverter/defibrillator (PCD)corresponding to any of the various commercially-available implantablePCDs. Those and other alternative implantable devices may be employedusing the present disclosure in that such devices may employ or bemodified with circuitry and/or systems according to the presentdisclosure. Examples of such alternative devices of IMD 20 may be animplantable nerve stimulator or muscle stimulator. In fact, the presentdisclosure is believed to find wide application in any form of anelectrical device, and is further believed to be particularlyadvantageous where low power consumption is desired, particularly inbattery powered devices.

In general, IMD 20 includes a hermetically-sealed enclosure thatincludes a power source and circuitry to control therapy delivery toheart 12. The circuitry may be implemented in discrete logic and/or mayinclude a microcomputer-based system with A/D conversion.

FIG. 2 provides a simplified block diagram of exemplary circuitry 30that may be housed within the IMD 20 and is configured to produce pulsesthat are used to pace the heart; i.e., cause a depolarization of theheart tissue or issue a defibrillation pulse to shock the heart fromarrhythmia to a normal heart beat. Circuitry 30 is shown to include apower source 32 electrically coupled to a controller 34 and a shockingcircuit 36. Although circuitry 30 depicts three components, it will beappreciated that fewer or more components may be employed. Power source32 is configured to provide operating power to controller 34 andshocking circuit 36 and is preferably capable of operating at lowcurrent drains over a long duration and at high current pulses whenshock delivery to patient 10 is required. Any one of numerous types ofappropriate batteries may be used, such as, for example lithium/silvervanadium oxide batteries.

Controller 34 controls the delivery of energy through lead 22 (shown inFIG. 1 ). Controller 34 is preferably configured to determine when,where, and for what duration the energy may be delivered. In thisregard, any one of numerous types of suitable control circuitry, such asmicroprocessors; or circuitry including memory, logic and timingcircuitry; and I/O circuitry, may be employed.

Shocking circuit 36 is configured to generate low or high energyshocking pulses and to deliver the shocking pulses to patient 10 inresponse to control signals from controller 34. In this regard, shockingcircuit 36 includes a transformer assembly 38 that is coupled to atleast one capacitor 40, which is in turn coupled to a delivery switch42. Transformer assembly 38 is configured to operate according to theprinciples of a flyback inductor, and thus, receives voltage from powersource 32 to be converted to an appropriate voltage to be used byshocking circuit 36. The converted voltage is stored in capacitor 40, orany other suitable energy storage device, until the shocking pulse isready to be delivered. When ready, delivery switch 42 is switched froman off position to an on position thereby routing the shocking pulse tothe appropriate leads.

Referring now to FIG. 3A, a cross-sectional view of a transformerassembly 38 a in accordance with an embodiment of the disclosure isdisclosed. The transformer assembly 38 a is shown having a substrateunit 50 and an upper magnetic core 56 disposed over an exterior surfaceof the substrate unit 50. By way of illustration, the portion of theexterior surface to which the upper magnetic core 56 will be referred toas a top surface 53 a. An encapsulant material 54 is dispensed overexterior surfaces of the upper magnetic core 56 and the substrate unit50 for encapsulation of both the upper magnetic core 56 and substrateunit 50. In an embodiment, the encapsulant material 54 is furtherdispensed between one or more gaps formed between the substrate unit 50and the upper magnetic core 56 to eliminate the air gaps therebetweenand form an air tight seal. The encapsulant material 54 is formed toexpose a surface of the upper magnetic core 56 that is parallel to thetop surface of the substrate unit 50. The transformer assembly 38 afurther includes a lower magnetic core 58 that is bonded to an exteriorsurface of the substrate unit 50. For ease of discussion, the portion ofthe exterior surface to which the lower magnetic core 58 is bonded willbe referred to as a bottom surface 53 b.

The substrate unit 50 includes one or more electronic components 52 thatmay be partially or fully embedded into the substrate unit 50. Theelectronic components 52 may include a set of primary windings 59 andsecondary windings 61. In one configuration, the primary windings 59 aredisposed in an overlapping relation to the secondary windings 61. Inanother embodiment, the primary windings 59 may be configured in anon-overlapping relation to the secondary windings 61. A pair ofterminal connectors 60 is provided for coupling to the primary windings59 and the secondary windings 61, respectively. The terminal connectors60 may be formed at least partially on the bottom (and/or top) surface53 a-b of the substrate unit 50 as the external terminals for connectingthe transformer assembly 38 a to other components of the IMD. As such,the terminal connectors 60 are exposed to facilitate the coupling of thetransformer assembly 38 a to other components of the IMD 20. Forexample, the primary windings 59 may be coupled to the battery (FIG. 2 )and the secondary windings 61 may be coupled to the capacitors (FIG. 2).

FIG. 3B illustrates a cross-sectional view of an alternative transformerassembly 38 b. For ease of description, the elements of transformerassembly 38 b corresponding to those of transformer assembly 38 a arenumbered with identical reference designators. The reader is referred tothe preceding description of FIG. 3A for a full discussion pertaining tothose components.

In the embodiment of FIG. 3B, the transformer assembly 38 b includescircuitry 62 that is coupled to the substrate unit 50. In an embodiment,the circuitry 62 may be coupled on the substrate unit 50 adjacent to theupper magnetic core 56 and lower magnetic core 58. The specificcomponents included in circuitry 62 may vary and provide a variety offunctionalities. For example, some of the functionality of IMD 20 may beembodied in the components of circuitry 62. The components of circuitry62 are electrically coupled to one or more terminals 64. The terminals64 are connectable with additional components of IMD 20.

FIG. 4 depicts a cross-sectional view of another transformer assembly 38c. Transformer assembly 38 c includes a substrate unit 50. A portion ofthe substrate unit 50 is formed having embedded electronic components 52that may include a set of primary windings and secondary windings. Thesubstrate unit 50 further includes a pair of terminal connectors 60 thatare electrically coupled to the electronic components 52. Among otherthings, the terminal connectors 60 facilitate coupling of the primaryand secondary windings to other components of the IMD 20. For example,the primary windings may be coupled to the battery (FIG. 2 ) and thesecondary windings may be coupled to the capacitors (FIG. 2 ).

The substrate unit 50 is embedded within a unitary core 57. In oneembodiment, the unitary core 57 may be formed having a uniform thicknessaround opposing major surfaces 53 a, 53 b of the substrate unit 50. Aswill be described with reference to FIGS. 7A-B, core 57 encapsulatingthe substrate unit 50 is formed by a molding process that utilizes apolymer bonded magnetic compound. Briefly, the molding processfacilitates fabrication of custom dimensioned cores having package sizesthat are smaller relative to those achievable with conventional cores.The packages may be molded having excess (sacrificial) material thatfacilitates handling during the various processing tasks, with thematerial being removed during a grinding process to obtain desiredpackage dimensions.

FIGS. 5A to 5E depict cross-sectional views during tasks associated witha method for fabricating a transformer according to an embodiment of thedisclosure such as that shown in FIGS. 3A and 3B. A substrate 44 (e.g.,a printed wiring board or a semiconductor wafer) having a plurality ofsubstrate units (e.g., 50 a, 50 b) is temporarily attached to a carrierplate 102. In the illustrative embodiment, the dotted line 100demarcates the location where the substrate/wafer board 44 having aplurality of substrate units 50 a-b would be sawed to separate theindividual transformer units upon completion of the assembly. In oneembodiment, the carrier plate 102 is made of stainless steel and has athickness of, for example, between 2 and 10 mm. The shape and size ofthe carrier plate 102 may correspond to that of the substrate 44. Thesubstrate 44 is attached to the carrier plate 102 using an adhesivelayer 104 that has first and second opposing surfaces 106, 108, with abottom surface 48 of the substrate being mounted to the first opposingsurface and a surface 114 of the carrier plate being mounted to thesecond opposing surface. Although not specifically shown, the adhesivelayer 104 may comprise a thermal release tape that includesthermally-degradable adhesive. Another example of the adhesive layer 104may comprise a solvent-soluble adhesive, in which case, the carrierplate 102 is made of a porous material that allows a solvent to passtherethrough, such as a composite material of aluminum oxide embedded ina glass matrix.

In another embodiment, the substrate 44 may be attached to asingle-sided PSA release tape that is not directly supported by acarrier plate. In the embodiment, the PSA release tape is suspended on awafer mounting ring, and the substrate 44 is attached to the PSA releasetape by vacuum lamination. Support for the PSA release tape andsubstrate is provided by a mold chase during molding.

The substrate 44 may comprise a standard G-10 board that is used forprinted circuit boards, which include a copper conductor layer 51 etchedon the bottom surface of the substrate. Other suitable materials for thesubstrate include metals, ceramics, plastics, polymers, and combinationsthereof. The substrate 44 is formed having electronic components 52 thatmay be disposed on a top surface 46, or partially embedded, or fullyembedded into the substrate material. In the simplest form, theelectronic components 52 may comprise a set of windings, including bothprimary and secondary windings 59, 61. Each set of the primary andsecondary windings 59, 61 may be coupled to terminal connectors 60 thatare formed on the bottom (and/or top) surface 53 b of each substrateunit horizontally-adjacent to the windings.

As is shown in the cross-sectional view, the electronic components 52are arrayed to define depressions 68 that extend vertically, in relationto the top surface 53 a, into the body of the substrate 44. Theexemplary embodiment depicts the depressions 68 being arrayed in theform of an “E” 110. Although the illustrative embodiment depicts thedepressions 68 being formed through the entire length of the body, it iscontemplated that in other embodiments the depressions may alternativelybe formed only partially into the body of the substrate.

FIG. 5B illustrates an upper core 56 that is placed over the top surface53 a of each of the substrate units 50. In the illustrative embodiment,the upper core 56 is an “E” core and legs 66 are disposed within thedepressions 68 formed on the substrate unit 50. As such, the upper core56 may be selected having dimensions that enable the upper core to beplaced over the top surface 46 of the substrate 44. The dimensions ofthe legs 66 of the upper core 56 are also selected to fit within thedepressions 68 of the substrate unit 50. In other embodiments, theconverse relationship may be defined in the design criteria—i.e., thesubstrate unit 50 including the depressions 68 may be formed to matchthe dimensions of a pre-selected upper core. The upper core 56 may be amagnetic core formed from ferro-magnetic material, amorphous metal orother advanced materials as is known in the art.

Next, as illustrated in FIG. 5C, an encapsulant material 54 is dispensed(e.g., formed, injected, or deposited) over the top surface 46 of thesubstrate 44 and the exposed portions of the upper core 56 including thegaps between the upper core and the substrate. In one embodiment, theencapsulant material 54 may be deposited having a consistentcross-sectional area around the substrate/core assembly. For example,the encapsulant material 54 may be deposited to define a depth (orthickness) of, for example, approximately 1 mm around the substrate/coreassembly. In one embodiment, the encapsulant material 54 is anelectrically insulative material such as, a silica-filled epoxy, with afinal cure temperature of, for example, between 140 and 150 degreesCentigrade (C). Other embodiments may use other types of encapsulantmaterials that have higher filler content or that are low moduluscompounds. The carrier plate 102, along with the various componentssupported thereon, is subsequently heated or “baked” in, for example, anoven. In one embodiment, the baking is performed at a temperature ofapproximately 100 degrees C. for 60 minutes.

Subsequent to, at least partial, curing (e.g., 40% cure), the exposedencapsulant material 54 undergoes a grinding (and/or polishing,abrasion, milling) process to reduce the thickness of the moldedassembly (encapsulant material and core) to a reduced, or thinnedthickness as is shown in FIG. 5D. In other words, the molding processmay include forming during the molding process a package that is largerthan the desired final package to facilitate handling with the grindingprocess being performed to achieve the desired package dimensions. Inthe depicted embodiment, the grinding process is performed using apolishing or grinding head (or polishing element) that is placed intocontact with and pressed against the molded assembly while being rotatedand moved across the exposed surface of the assembly.

Turning next to FIG. 5E, the adhesive layer 104 is separated from thesubstrate 44 which in turn separates or unmounts the substrate from thecarrier plate 102. The separation may be performed by, for example,exposing the adhesive to a solvent for a solvent-soluble adhesive, orheat, for a thermally degradable adhesive. Removal of the adhesive layer104 exposes the terminals of the transformer assembly that are disposedon the bottom surface 53 b of the substrate unit 50.

Additionally, a lower core 58 is attached to the bottom surface 53 b ofeach of the substrate units 50. The lower core 58 is placed in anoverlapping relation to the upper core 56 and away from the exposedterminals 60. The lower core 58 may be formed from materials similar tothose of the upper core 56 including, but not limited to, magneticmaterials. The lower core 58 may be configured, for example, as an “I”core element and may be selected having at least a length-wise dimensionthat is matched with the length of the upper core 56. Without intendingto be limiting, the fixation between the lower core 58 and the substrateunit 50 may be achieved through a pressure sensitive adhesive (PSA)compound. However, it should be noted that any other type of adhesiontechnique and/or adhesive compound may be utilized to achieve thebonding between the lower core 58 and the substrate unit 50 a-b.

In embodiments in which the substrate 44 includes more than onesubstrate unit 50 a-b, the substrate units are singulated along lines100, for example, into individual units, such as those shown in FIGS. 3Aand 3B. Singulation may be performed through, for example, sawing, orlaser etching, or chemical singulation or any other methods known in theart.

Turning to FIGS. 6A-6C, tasks for assembly of a transformer inaccordance with an alternative embodiment are depicted. The tasks may beperformed prior to the singulation of the substrate into individualsubstrate units. In FIG. 6A, a plurality of conductive pads 112 areconnected to the substrate 44, such that one pad is coupled to each ofthe terminal connectors 60. The conductive pads 112 may be made ofAluminum (Al) or Copper (Cu) or any other conductive material withproperties to enable soldering. In some embodiments, one or more surfacemountable components, such as an integrated circuit (IC) (not shown),may also be coupled to the substrate unit's bottom surface 53 b havingelectrical terminals for connection of the IC to other components of theIMD.

Next in FIG. 6B, a carrier plate 102 is attached to the top surface 53 aof the molded substrate. An adhesive layer 104 may be used as describedwith reference to FIG. 5B to attach the carrier plate 102 to the topsurface 53 b. An encapsulant material 114, such as that described above,is subsequently dispensed over the bottom surface 53 b of the substrateassembly, which includes the adhered lower core 58. In embodimentshaving the surface mountable component, the encapsulation of the bottomsurface 53 b is performed to also encapsulate such surface mountablecomponents. Dispensing and curing of the encapsulant material 114 may beperformed in accordance with the discussion above in conjunction withFIG. 5C.

Subsequently, after curing of the encapsulant material 114, the exposedencapsulant material 114 on the bottom surface 53 b of the moldedassembly undergoes a grinding (and/or polishing, abrasion, milling)process to reduce the thickness of the molded assembly (encapsulantmaterial and core) to a reduced, or thinned thickness as is shown inFIG. 6C. The grinding also exposes the lower core 58 and the conductivepads 112 (and the IC terminals in embodiments having one or more ICs).In both grinding processes of FIGS. 6C and 5D, the lower and upper cores58, 56 may also be thinned to a desired thickness, if appropriate. Thetop surface 53 a is subsequently separated from the carrier plate 102 bydetaching the adhesive layer 104.

According to another embodiment of the present disclosure, anothermethod for assembling a transformer, such as that depicted in FIG. 4 ,is disclosed which is illustrated in the FIG. 7A and FIG. 7Bcross-sectional views of exemplary processing tasks. In this method, ahomogeneous core 57 is integrally formed around a substrate unit 50 thatincludes a set of windings for the transformer. Unlike conventionaltransformer cores, the method of the embodiments described withreference to FIGS. 7A and 7B yield a homogenous transformer core 57 thatcan be custom-made with any desired shape or size and tailored toindividual specifications and electrical performance characteristics.

Formation of the homogeneous core 57 to encapsulate the substrate unit50 in accordance with embodiments of the method enables customization ofthe thickness of the core's sections on opposing surfaces of thesubstrate unit 50. For example, the thickness around opposing surfacesmay be formed to be uneven based on desired electrical performancecharacteristics of the transformer. In yet another example, the core 57may be formed by distributing the encapsulant material uniformly aroundthe substrate unit to define a consistent cross-sectional area for themagnetic path.

As shown in FIG. 7A, a mold chase 80 is provided for formation of thecore 57. The mold chase 80 includes an upper mold chase 82 having anupper cavity 116 and a lower mold chase 84 having a lower cavity 118.Upper mold chase 82 and lower mold chase 84 may be formed withcorresponding cavity dimensions such that a continuous or contiguouscentral cavity 86 is formed when the upper mold chase 82 is placed overthe lower mold chase 84. Additionally, each of the upper and lowercavities 116, 118 may be configured in a shape and size corresponding tothat of a desired upper and lower core, respectively. Together, theupper and lower cavities 116, 118 define the central cavity 86 intowhich a substrate 44 having one or more substrate units 50 is receivedfor encapsulation. Each substrate unit 50 or substrate 44 having aplurality of adjoining substrate units 50 is placed over the top surface120 of the lower mold chase 84, with the upper mold chase 82 beingseparated from the lower mold chase 82. As discussed above, thesubstrate unit 50 is formed having one or more electronic components 52that include a set of primary and secondary windings.

In one example, the mold chase 80 includes a receptacle 88 that isformed, for example, at a central portion of the lower mold chase 84.The receptacle 88 includes a hollow interior that is in fluidcommunication with a first opening at an outer surface of the lower moldchase 84 and a second opening into the lower cavity. A plunger 90 isdisposed within the receptacle 88, and in use, the plunger 90 ismoveable within the receptacle in a direction toward the second openingto transfer an encapsulant material 54 held within the receptacle 88into the central cavity 86. As such, the plunger 90 may include a headplate 92 that is dimensioned to fit circumferentially-around acylindrically-shaped receptacle, for example, with a pin 94 that isutilized for force transfer. The plunger 90 may be operated manually orunder a hydraulic pressure.

The encapsulant material 54 may be held in the receptacle in a molten orliquefied state to facilitate the transfer from the receptacle into thecentral cavity 86 and to ensure complete encapsulation of the substrateunits. Such encapsulation eliminates air gaps that may otherwise beformed between the substrate unit and the core.

The material selection for the encapsulant material is based on desiredelectrical functionality of the transformer and electrical properties ofthe core. Without intending to be limiting, the materials may includepolymer bonded magnetic compounds formed, for example, by mixing apolymer binder with magnetic powder. The polymer binder can be eitherthermoplastic or thermoset. Thermoplastic polymer binders include LiquidCrystal Polymer (LCP), polyamine (e.g., Nylon 6), andpolyphenylenesulfide (PPS) all of which are injection moldablematerials. Thermoset binders can either be transfer molded orcompression molded. Epoxy molding compounds are used in a transfermolding process while Phenolic and diallyl phthalate (DAP) resins can beused in a compression molding process. Soft magnetic powder can beMagnetics Molypermalloy Powder (MPP), soft ferrite, powdered iron,HI-FLUX, sendust, or Kool Mμ. Examples of polymer bonded magneticcompounds are commercially available from Arnold Magnetic TechnologiesCorporation of Rochester, NY.

Referring again to FIG. 7A, one or more outlet vents 96 are formed onthe mold chase 80 to facilitate dispensing of the encapsulant material54. In the illustrative embodiment, the dispensing of the encapsulantmaterial 54 is performed in a transfer phase during which theencapsulant material 54 is expelled from the receptacle into the centralcavity 86. The outlet vents 96 prevent a build-up of pressure inside thecentral cavity 86 that would otherwise create an opposing force thatcounteracts the flow of the encapsulant material into the cavity 86.

Turning next to FIG. 7B, the encapsulant material 54 is illustratedhaving being dispensed into the central cavity 86 for encapsulation ofthe substrate. The dispensing of the encapsulant material 54 into thecavity is performed while ensuring complete coverage of each substrateunit. This can be done by rapidly filling the central cavity 86,generally prior to initiation of the curing of the encapsulant material.In other embodiments, the encapsulant material 54 may be dispersedthrough a plurality of receptacles for even faster encapsulant filling.After the encapsulant material 54 is dispensed into the cavity 86, themolded assembly is cured.

The specifics pertaining to the curing of the encapsulant material curewill depend on the properties of the selected material. For example, theencapsulant material may cure fairly rapidly without any processingtasks in one embodiment. In other words, allowing the molded assembly tosettle without more may permit the encapsulant material to betransformed into a solid state while it is held in the mold chase. Inother embodiments, further processing tasks may be performed to enhancecuring of the encapsulant material. For example, the mold chase may becooled to a temperature that causes the encapsulant material to betransformed into a solid state, or the material may be heated to atemperature that causes the encapsulant material to harden (e.g., above200° C.), or a chemical reaction may be performed, or the encapsulantmaterial may be irradiated, or any other processing that causes theencapsulant material to harden based on its properties.

Subsequent to the curing cycle the molded assembly is ejected from themold chase by separating the upper mold chase 82 from the lower moldchase 84. The molded assembly yielded includes one or more substrateunits 50 encapsulated by an encapsulant material that becomes rigid todefine the core 57, as illustrated in FIG. 4 . Similar to theembodiments described in the figures above, the molded assembly may beformed having dimensions that are larger than the dimensions desired fora final package to facilitate handling. The molded assembly may furtherundergo a grinding (and/or polishing, abrasion) process to reduce thethickness of the core to a reduced, or thinned thickness. Further, inembodiments in which the substrate includes more than one substrateunit, the substrate units may be singulated to yield individualsubstrate units as shown in FIG. 4 .

It should be noted that the description of the tasks in FIGS. 7A and 7Bis merely exemplary of one molding process that can be used for forminga transformer assembly by encapsulating a substrate with an encapsulantmaterial to yield a continuous high permeability magnetic path. Thoseskilled in the art will recognize that the principles described in theabove tasks associated with a transfer molding process, may be embodiedin other molding processes such as compression molding or injectionmolding depending on the polymer bonded magnetic compound.

Moreover, the foregoing assembly methods describe construction of planartransformer assemblies formed with a substrate having one or more setsof primary windings and secondary windings. The techniques described inthe disclosure may, however, be suitably applied to assembly ofnon-planar transformers such as those having the primary and secondarywindings that are wound on a bobbin.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. In the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. A method of forming a transformer assemblycomprising: attaching a bottom surface of a substrate to a carrierplate, wherein the substrate comprises a plurality of substrate units,wherein a bottom surface of each substrate unit of the plurality ofsubstrate units forms the bottom surface of the substrate; disposingelectronic components on a top surface of the substrate or at leastpartially embedded in material of the top surface of the substrate,wherein at least one electronic component comprises primary andsecondary windings, wherein a top surface of each substrate unit of theplurality of substrate units forms the top surface of the substrate;disposing an upper magnetic core over the top surface of each substrateunit of the plurality of substrate units and the electronic components;dispensing encapsulant material over the top surface of the substrateand exposed portions of the upper magnetic core and gaps between theupper core and the substrate to form a molded substrate; grindingportions of the encapsulant material and the upper magnetic core to forman upper planar surface of the molded substrate, wherein the upperplanar surface comprises an exposed surface of the encapsulant materialand an exposed surface of the upper magnetic core; removing thesubstrate from the carrier plate; and disposing a lower magnetic core tothe bottom surface of each substrate unit of the plurality of substrateunits.
 2. The method of claim 1, further comprising disposing a secondcarrier plate on the upper planar surface of the molded substrate. 3.The method of claim 2, further comprising dispensing additionalencapsulant material over the bottom surface of the substrate and thelower magnetic core.
 4. The method of claim 3, further comprising atleast partially curing the additional encapsulant material.
 5. Themethod of claim 4, further comprising grinding the additionalencapsulant material and the lower magnetic core to form a lower planarsurface of the molded substrate, wherein the lower planar surfacecomprises an exposed surface of the additional encapsulant material andan exposed surface of the lower magnetic core.
 6. The method of claim 5,wherein grinding portions of the additional encapsulant material and thelower magnetic core comprises thinning the lower magnetic core disposedon the bottom surface of each substrate unit to a desired thickness. 7.The method of claim 5, further comprising removing the second carrierplate from the upper planar surface of the molded substrate.
 8. Themethod of claim 1, further comprising singulating the plurality ofsubstrate units to provide individual substrate units.
 9. The method ofclaim 1, further comprising at least partially curing the encapsulantmaterial prior to grinding portions of encapsulant material and theupper core.
 10. The method of claim 9, wherein at least one of theencapsulant material or additional encapsulant material comprises apolymer bonded magnetic material.
 11. The method of claim 1, whereinattaching the bottom surface of the substrate to the carrier platecomprises attaching the bottom surface of the substrate to a firstopposing surface of an adhesive layer and attaching a surface of thecarrier plate to a second opposing surface of the adhesive layer. 12.The method of claim 11, wherein the adhesive layer comprises a thermalrelease tape comprising a thermally-degradable adhesive.
 13. The methodof claim 1, wherein disposing the lower magnetic core comprises adheringthe lower magnetic core to the bottom surface of each substrate unit.14. The method of claim 1, wherein grinding portions of the encapsulantmaterial and the upper magnetic core comprises thinning the uppermagnetic core disposed over the top surface of each substrate unit to adesired thickness.
 15. The method of claim 1, further comprising formingone or more terminal connectors on at least one of the top surface orbottom surface of each substrate unit of the plurality of substrateunits, wherein the primary and secondary windings of the at least oneelectronic component is coupled to a terminal connector of the one ormore terminal connectors.
 16. The method of claim 15, further comprisingconnecting a plurality of conductive pads to the substrate, wherein eachterminal connector is coupled to a conductive pad of the plurality ofconductive pads.
 17. The method of claim 1, wherein at least oneelectronic component of each substrate unit of the plurality ofsubstrate units comprises primary and secondary windings.